A New Carrollton man shot and killed a home invader Tuesday night as the intruder broke through the glass panes of the man's front door and reached through to unlock it, officials and law enforcement sources said.

The 27-year-old resident, whom police did not identify because he is not charged with a crime, was standing in the doorway with a shotgun while the other man, apparently a stranger, tried to break in, police officials and law enforcement sources said.

Someone inside the house, in the 7400 block of Riverdale Road in New Carrollton, called 911 to report the incident as it was happening, and the residents screamed at the intruder that he should leave as he continued to force his hand through the glass, said Maj. Andrew Ellis, public affairs commander for the Prince George's County police.

"Initially, it appears to be a justifiable homicide," Ellis said.

Officers were called to the home about 8:40 p.m., authorities said. By the time they arrived, Ellis said, the intruder was dead on the front porch, shot by the 27-year-old, who lived in the house with his parents.

A woman who answered the phone at the home said her husband had prohibited the family from talking about the case while the police investigation was underway. Asked whether a reporter could talk to her son - who seemed to be the "hero" in the case - she said: "There was no hero. The only thing I can tell you is we are thankful we are alive."

Police identified the man who was killed as Clyde Antwone Rosevelt Howard, 30, of the 6800 block of Riverdale Road in New Carrollton. A woman who answered the door at his apartment, just down the street from where he was shot, declined to comment.

Broken glass was still visible in the door windows Wednesday. The scene seemed an unusual spot for a home invasion. The single-family home is next to a busy four-lane highway and across the road from a chiropractor's office and an open field. There is no sidewalk in front of it.

Ellis said he does not know why Howard picked the house, and investigators do not think he knew the people inside. Online court records show that Howard had faced drug and alcohol charges in the past and had been convicted of manufacturing and distributing drugs.

"Why the suspect targeted the victims' house, we don't know right now," Ellis said. "It appears to be completely random."

Ellis said there was "no indication" that the gun used in the killing was obtained illegally. A law enforcement source said evidence at the scene supported a finding of justifiable homicide. The glass from the door, for example, was pushed inward, indicating that someone had tried to force his way through from the outside, and residents of the home were cooperating with investigators, the source said.

Also on Wednesday, the medical examiner ruled that a woman found dead Friday in the Capitol Heights area near the D.C. line was a homicide victim, bringing the county's total for the year to 13.

The woman's partially clothed body was found just after 8 a.m. Friday across from a scrap yard in the 1700 block of Olive Street, authorities and sources said. Police have released few details about the case, including how the woman died, contending that giving out the information would jeopardize the investigation.

Ellis said the woman's body showed no obvious signs of trauma, such as wounds from a stabbing, shooting or beating.

Ellis identified the woman as Alitha Mae Jenkins, 51, of the 2400 block of Kent Village Place in the Capitol Heights area. He said she was unemployed and was known to frequent the area where her body was found.

Online court records show that Jenkins had an extensive criminal history, including convictions for theft and prostitution-related offenses.

Police also have identified the University of Maryland student slain Tuesday during an apparent drug-related robbery in the Adelphi area as Justin Vance DeSha-Overcash, 22. Friends said that he had lived in North Carolina and Pennsylvania and that he was a physics and astronomy major who produced his own music and played intramural sports. He was in his final year in school, friends said.